This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Elderly people are at higher risk than young adults of suffering from morbidity and mortality associated with infectious diseases, and this is primarily due to the declining immune system, or immunosenescence, that occurs during aging. Immunosenescence also contributes to a decline in vaccine efficacy in the elderly, which poses a tremendous challenge to public health. The purpose of this study is to apply a nonhuman primate model of aging to determine if older rhesus macaques ( 14 years of age) with lower levels of na[unreadable]ve T cells and function (ie. proliferation and turnover rates) will express lower immune responses to vaccination than age-matched older monkeys that have relatively higher levels of na[unreadable]ve T cells and function. During the biannual inventory evaluations of nonhuman primates at TNPRC, T cell phenotype profiles and immune function assays are being performed to assess the immune status of the older animals. In addition, a study is currently underway to compare the efficacy to two types of influenza vaccine, virus-like particles (VLP) and the current seasonal (2008-2009) TIV vaccine, in young and older adult rhesus macaque monkeys. The hypothesis of this study is that VLP influenza vaccination will prove more effective than the commercial TIV vaccine in young adult and older adult rhesus macaques. Groups of young adult rhesus macaques (5 [unreadable]9 years old) and older adult rhesus macaques (14 years or older) were selected, pre-screened for being seronegative to influenza H1N1, and vaccinated with either influenza virus like particles (VLP) or the commercial TIV vaccine two times. One set of monkeys in each age group remained unvaccinated (i.e. sham vaccinated). The monkeys will then be inoculated with influenza H1N1 followed by nasal wash, bronchoalveolar lavage, and venipuncture to test viral levels, cytokine production, and antibody expression. Clinical signs also will be monitored (body temp, weight, activity) daily for one week after challenge.